"Clean rooms" are required in hospitals, laboratories, and industrial operations wherever it is necessary to maintain a work environment substantially free of particles suspended in the air. The most common form of these installations involves a group of filter modules defining a major portion of the ceiling area of a room, which provide an inflow of filtered air proceeding to a convenient outlet, usually near the floor. Each of the modules is essentially a housing accommodating a conventional filter element having a rectangular box-like configuration. These are standard, and must necessarily be replaced frequently. Since "clean" atmospheric conditions are defined in terms of suspended particles having dimensions on the order of a few microns, it is of crucial importance that the modular units provide an absolute minimum of passages or recesses through or in which such particles can move or accumulate. The outlet opening from which air emerges after moving through the filter element is normally covered by a protective grille, which becomes an inviting location for particles to accumulate during periods in which the air may be stagnant within the room. When the air flow through the filter modules is turned on, such accumulations are obviously subject to disturbance and discharge back into the room. Recesses at fastenings that are exposed to the room also present problems. Replacement of the filter element involves withdrawing it through the opening normally occupied by the grille, and replacing it in the reverse of this procedure. Such action also obviously tends to disturb any accumulations of particles that may have found a way into recesses of any description in the adjacent area.
The importance of "clean room" installations has generated enough attention to produce quite a number of structural arrangements in the filter modules. These have displayed a considerable difference one from another in their functioning characteristics with regard to cost and the relative tendency to entrap and redistribute particles in the room space during service and maintenance operations, and at times when the air flow system is turned on after periods of stagnation.
The present application presents an improvement on the U.S. Pat. No. 4,088,463 of Irwin M. Smith, issued on May 9, 1978. That application is now owned by the present applicant. Problems encountered during the removal and replacement of the filter modules, and in cleaning the grilles in the structure disclosed in the Smith application, have resulted in the present development.